This is the first systematic philosophical and conceptual study of the notion of a social practice. Raimo Tuomela explains social practices in terms of the interlocking intentions of the agents; he shows how social practices (for example customs and tradition) are "building blocks of society"; and he offers a clear and powerful account of the way in which social institutions are constructed from these building blocks as established, interconnected sets of social practices. His analysis is based on the novel concept of shared "we-attitudes," which represent a weak form of collective intentionality, and he makes instructive connections to major topics and figures in philosophy and the social sciences. His book will be of interest to a wide range of readers in philosophy of mind, philosophy of social science, psychology, sociology, and Artificial Intelligence.